Isaac was Lord Mayor of London when war broke out and also sat in the commons as a member of the Long Parliament. This picture is from “A True Declaration and Just Commendation of the Great and Incomparable Care of the right Honourable Isaac Pennington, Lord Mayor of London in Advancing and promoting the Bulwarkes and Fortifications about the City and Suburbs”, printed April 1643.
The Lord Mayor wears an impressive brimmed hat and fur lined gown over a doublet with his chain of office across his chest. He’s also sporting a starched ruff collar, something that was a little old fashioned by this time but seems to have been retained as part of official regalia.
The 1640s Picturebook 